1. Field of the Invention
The present invention relates to an optical disc, and more particularly, to an optical disc having an enhanced recording density, and fabrication of the optical disc is facilitated and tracks are narrowed.
2. Description of the Related Art
In general, a near field recording drive is used for recording data on a disc or reproducing data from the disc in which an optical spot focused on the disc forms a near field. In the near field recording drive, a light flying head and a disc are spaced from each other by a predetermined interval, in order to record, reproduce and erase the data with respect to the disc to which a near field is formed. This technology is disclosed in detail in U.S. Pat. No. 5,470,627, which will be briefly described below with reference to FIG. 1.
FIG. 1 is a view for explaining a general near field recording drive. The FIG. 1 apparatus shows a state where a light flying head supported in a suspension 12 of a swing arm 10 is floated from the surface of an optical disc 40. The light flying head includes an objective lens 30 and a slider 31 mounting the objective lens 30 thereon, and a magnetic coil (not shown). A prism 20 with reflective surfaces 21 are positioned at an end of the light flying head. The optical disc 40 of FIG. 1 is a double-sided recording disc, in which two sheets of discs each having a one-sided recording surface are assembled with each other. The disc 40 has grooves 50 and lands 60 formed on the top and bottom surfaces of a substrate 45.
A recording/reproducing operation of the FIG. 1 apparatus will be described. In the FIG. 1 apparatus, the slider 31 rests in a parking zone (not shown) toward the inner diameter of the optical disc 40 when recording and reproducing operations are not performed. At the recording and reproducing times, the slider 31 is floated from the parking zone and moves to a data region of the optical disc 40, in order to perform the recording and reproducing operations. The reflective surfaces 21 reflect laser light 11 from a light source (not shown) and the objective lens 30 refracts laser light 11 emitted from a light source (not shown) and emits the laser light toward the optical disc 40. The light emitted from the objective lens 30 is focused in the form of an optical spot on the optical disc 40.
A near field is formed between the surface of the objective lens 30 on which the laser light 11 is focused and the optical disc 40. As a result, information is recorded on the optical disc 40 and read out from the optical disc 40 via the near field. That is, the light focused on the surface of the optical disc 40 becomes a heat source, to heat a recording layer of the optical disc 40 higher than a predetermined temperature. If a current flows through a magnetic coil during heating to thereby generate a constant magnetic field, the vertical component of the magnetic field forms a vertical magnetic sphere on a recording layer of the disc, to thereby perform a data recording. When the recorded data is reproduced, the light flying head irradiates laser light toward the surface of the optical disc 40 on the vertical magnetic sphere and reads data according to a deflection direction of the laser light reflected from the surface of the optical disc 40. That is, the reflective light reflected from the reflective layer coated on the surface of the optical disc 40 is incident to the objective lens 30. The tracking during recording and reproducing is possible as the patterns of the lands 50 and the grooves 60 formed on the substrate 45 are distinguished by the reflective layers.
A more detailed structure of the optical disc 40 used in the FIG. 1 apparatus is shown in FIG. 2. On the front and rear surfaces of the substrate 45 shown in FIG. 2 are formed grooves 50 and lands 60. On the grooves 50 and lands 60 are formed respective reflective layers 41, dielectric layers 42, recording layers 43 and protective layers 44, in sequence. In the case that pits are formed in the portion of the embossed lands 60 to perform a data recording, the grooves 50 are relatively formed in an engraved fashion. Here, the reflective layer 41 used for enhancing a reflective efficiency is coated in comparatively uniform thickness on the planar lands 60. However, the reflective layer 41 is not coated along the pattern of the grooves 50 in the narrowly engraved grooves 50. That is, in the case of the grooves 50, the reflective layer 41 is coated on the grooves 50 in a fashion where the former backfills the deep portion of the grooves 50, to accordingly vary the shape thereof. In the case that the dielectric layer 42, the recording layer 43 and the protective layer 44 as well as the reflective layer 41 are deposited in sequence, the grooves 50 are also deformed in a manner where deep portions are backfilled. Referring to FIG. 2, when the reflective layer 41, the dielectric layer 42, the recording layer 43 and the protective layer 44 are deposited on the substrate 45 having the grooves 50 thereon, it can be seen that the depths and the widths of the grooves 50 are deformed gradually.
As described above, since four or more layers are deposited on the substrate on which the grooves are formed in the optical disc, the grooves are backfilled with sputtering particles. As a result, a signal detected by a light flying head is feeble. Meanwhile, there is a method for equaling the groove width and deepening and narrowing the groove depth so that the signal detected by the light flying head becomes greater. However, this method makes disc fabrication difficult since a stamper for fabricating a basic form of a substrate should be fabricated in the form of an inverse V-shape.